Not all pagan keep permanent altars in their homes, and sometimes its because not everyone follows the same path. You can, however, provide a mixed family altar where everyone can combine their beliefs in one place.
You will need;
Mutual respect. Even if someone is Christian, you should respect that path and if they wish to set up a cross or similar religious symbol. Sharing respect strengthens family bonds, and helps encourage one another in their spiritual path.
Offering plate (or bowl, basket or other container). Here is where family can put prayers, promises, offerings, and other items in a single space for the Divine. I would suggest including a small pad of paper with pencil so members can jot down words when the need arises.
Offerings can often take many forms such as food, drink, incense, prayers, promises, shiny things, and intentions. You could even put money, and then the family can vote on where to send and which charity.
Season and holiday symbols. For instance, a spring altar might include eggs, flowers, but also crosses, and symbols of Christ’s resurrection. A winter solstice them can include symbols of the god, but also a nativity scene.
The family altars becomes a special place where members can individually or as a group, gather together for prayer and spiritual expression.